Organic electroluminescent materials and devices

ABSTRACT

Compounds including a ligand L according to Formula I devices containing the same and formulations including the same are described. 
     
       
         
         
             
             
         
       
     
     In Formula I, B is a 5 or 6-membered carbocyclic or heterocyclic ring; C is a condensed aromatic ring system having at least two carbocyclic or heterocyclic rings; A-B represents a bonded pair of carbocyclic or heterocyclic rings coordinated to a metal M via a nitrogen atom in ring A and an sp 2  hybridized atom X 6  in ring B; R A , R B  and R C  can represent no substitutions or the maximum substitutions available on the respective ring; X 1 , X 2 , X 3 , X 4 , X 5 , and X 6  are carbon or nd nitrogen, and X 7  is carbon; at least one of R A  and R C  substituents adjacent to the bond between A and C is not hydrogen; and the ligand is coordinated to a metal, having an atomic number greater than 40.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Patent Application Ser. No. 61/767,508, filed Feb. 21, 2013, the entire contents of which is incorporated herein by reference.

PARTIES TO A JOINT RESEARCH AGREEMENT

The claimed invention was made by, on behalf of and/or in connection with one or more of the following parties to a joint university corporation research agreement: Regents of the University of Michigan, Princeton University, University of Southern California, and the Universal Display Corporation. The agreement was in effect on and before the date the claimed invention was made, and the claimed invention was made as a result of activities undertaken within the scope of the agreement.

FIELD OF THE INVENTION

The present invention relates to compounds for use as emitters and devices, such as organic light emitting diodes, including the same.

BACKGROUND

Opto-electronic devices that make use of organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. Examples of organic opto-electronic devices include organic light emitting devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, illumination, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full color display. Industry standards for such a display call for pixels adapted to emit particular colors, referred to as “saturated” colors. In particular, these standards call for saturated red, green, and blue pixels. Color may be measured using CIE coordinates, which are well known to the art.

One example of a green emissive molecule is tris(2-phenylpyridine) iridium, denoted Ir(ppy)₃, which has the following structure:

In this, and later figures herein, we depict the dative bond from nitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as well as small molecule organic materials that may be used to fabricate organic opto-electronic devices. “Small molecule” refers to any organic material that is not a polymer, and “small molecules” may actually be quite large. Small molecules may include repeat units in some circumstances. For example, using a long chain alkyl group as a substituent does not remove a molecule from the “small molecule” class. Small molecules may also be incorporated into polymers, for example as a pendent group on a polymer backbone or as a part of the backbone. Small molecules may also serve as the core moiety of a dendrimer, which consists of a series of chemical shells built on the core moiety. The core moiety of a dendrimer may be a fluorescent or phosphorescent small molecule emitter. A dendrimer may be a “small molecule,” and it is believed that all dendrimers currently used in the field of OLEDs are small molecules.

As used herein, “top” means furthest away from the substrate, while “bottom” means closest to the substrate. Where a first layer is described as “disposed over” a second layer, the first layer is disposed further away from substrate. There may be other layers between the first and second layer, unless it is specified that the first layer is “in contact with” the second layer. For example, a cathode may be described as “disposed over” an anode, even though there are various organic layers in between.

As used herein, “solution processible” means capable of being dissolved, dispersed, or transported in and/or deposited from a liquid medium, either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed that the ligand directly contributes to the photoactive properties of an emissive material. A ligand may be referred to as “ancillary” when it is believed that the ligand does not contribute to the photoactive properties of an emissive material, although an ancillary ligand may alter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled in the art, a first “Highest Occupied Molecular Orbital” (HOMO) or “Lowest Unoccupied Molecular Orbital” (LUMO) energy level is “greater than” or “higher than” a second HOMO or LUMO energy level if the first energy level is closer to the vacuum energy level. Since ionization potentials (IP) are measured as a negative energy relative to a vacuum level, a higher HOMO energy level corresponds to an IP having a smaller absolute value (an IP that is less negative). Similarly, a higher LUMO energy level corresponds to an electron affinity (EA) having a smaller absolute value (an EA that is less negative). On a conventional energy level diagram, with the vacuum level at the top, the LUMO energy level of a material is higher than the HOMO energy level of the same material. A “higher” HOMO or LUMO energy level appears closer to the top of such a diagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled in the art, a first work function is “greater than” or “higher than” a second work function if the first work function has a higher absolute value. Because work functions are generally measured as negative numbers relative to vacuum level, this means that a “higher” work function is more negative. On a conventional energy level diagram, with the vacuum level at the top, a “higher” work function is illustrated as further away from the vacuum level in the downward direction. Thus, the definitions of HOMO and LUMO energy levels follow a different convention than work functions.

More details on OLEDs, and the definitions described above, can be found in U.S. Pat. No. 7,279,704, which is incorporated herein by reference in its entirety.

SUMMARY OF THE INVENTION

According to an embodiment, a compound is provided that includes a ligand L having the structure according to Formula I:

In Formula I:

-   -   B is a 5 or 6-membered carbocyclic or heterocyclic ring;     -   C is a condensed aromatic ring system having at least two         carbocyclic or heterocyclic rings;     -   A-B represents a bonded pair of carbocyclic or heterocyclic         rings coordinated to a metal M via a nitrogen atom in ring A and         an sp² hybridized atom X⁶ in ring B;     -   A-C represents a bonded, pair of carbocyclic or heterocyclic         rings;     -   R^(A) may represent mono, di, or tri substitutions, or no         substitution;     -   R^(B) may represent any number of substitution from mono to up         to the maximum possible number of substitution on ring B, or no         substitution;     -   R^(C) may represent any number of substitution from mono to up         to the maximum possible number of substitution on ring C, or no         substitution;     -   R^(A), R^(B), and R^(C) are independently selected from the         group consisting of hydrogen, deuterium, halide, alkyl         cycloalkyl, heteroalkyl, aralkyl, alkoxy, aryloxy, amino, silyl,         alkenyl, cycloalkenyl, heteroalkenyl alkynyl, aryl, heteroaryl,         acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile,         sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations         thereof;     -   X¹, X², X³, X⁴, X⁵, and X⁶ are independently selected from         carbon and nitrogen;     -   X⁷ is carbon;     -   at least one of R^(A) and R^(C) substituents adjacent to the         bond between A and C is not hydrogen; and     -   the ligand L is coordinated to the metal M having an atomic         number greater than 40.

According to another embodiment, a first device comprising a first organic light emitting device is also provided. The first device can include an anode, a cathode, and an organic layer, disposed between the anode and the cathode. The organic layer can include a compound including a ligand of Formula I. The first device can be a consumer product, an organic light-emitting device, and/or a lighting panel.

According to still another embodiment, a formulation that includes a compound including a ligand of Formula I is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does not have a separate electron transport layer.

FIG. 3 shows Formula I as disclosed herein.

FIG. 4 shows Formula II as disclosed herein.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed between and electrically connected to an anode and a cathode. When a current is applied, the anode injects holes and the cathode injects electrons into the organic layer(s). The injected holes and electrons each migrate toward the oppositely charged electrode. When an electron and hole localize on the same molecule, an “exciton,” which is a localized electron-hole pair having an excited energy state, is formed. Light is emitted when the exciton relaxes via a photoemissive mechanism. In some cases, the exciton may be localized on an excimer or an exciplex. Non-radiative mechanisms, such as thermal relaxation, may also occur, but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from their singlet states (“fluorescence”) as disclosed, for example. In U.S. Pat. No. 4,769,292, which is incorporated by reference in its entirety. Fluorescent emission generally occurs in a time frame of less than 10 nanoseconds.

More recently, OLEDs having emissive materials that emit light from triplet states (“phosphorescence”) have been demonstrated. Baldo et al., “Highly Efficient Phosphorescent Emission from Organic Electroluminescent Devices,” Nature, vol. 395, 15-154, 1998; (“Baldo-I”) and Baldo et al., “Very high-efficiency green organic light-emitting devices based on electrophosphorescene,” Appl. Phys. Lett., vol. 75, No. 3, 4-6 (1999) (“Baido-II”), which are incorporated by reference in their entireties. Phosphorescence is described in more detail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporated by reference.

FIG. 1 shows an organic light emitting device 100. The figures are not necessarily drawn to scale. Device 100 may include a substrate 110, an anode 115, a hole injection layer 120, a hole transport layer 125, an electron blocking layer 130, an emissive layer 135, a hole blocking layer 140, an electron transport layer 145, an electron injection layer 150, a protective layer 155, a cathode 160, and a barrier layer 170. Cathode 160 is a compound cathode having a first conductive layer 162 and a second conductive layer 164. Device 100 may be fabricated by depositing the layers described, in order. The properties and functions of these various layers, as well as example materials, are described in more detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which are incorporated by reference.

More examples for each of these layers are available. For example, a flexible and transparent substrate-anode combination is disclosed in U.S. Pat. No. 5,844,363, which is incorporated by reference in its entirety. An example of a p-doped hole transport layer is m-MTDATA doped with F₄-TCNQ at a molar ratio of 50:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. Examples of emissive and host materials are disclosed in U.S. Pat. No. 6,303,238 to Thompson et. al., which is incorporated by reference in its entirety. An example of an n-doped electron transport layer is BPhen doped with Li at a molar ratio of 1:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. U.S. Pat. Nos. 5,703,436 and 5,707,745, which are incorporated by reference in their entireties, disclose examples of cathodes including compound cathodes having a thin layer of metal such as Mg:Ag with, an overlying transparent, electrically-conductive, sputter-deposited ITO layer. The theory and use of blocking layers is described in more detail in U.S. Pat. No. 6,097,147 and U.S. Patent Application Publication No. 2003/0230980, which are incorporated by reference in their entireties. Examples of injection layers are provided in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety. A description of protective layers may be found in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210, a cathode 215, an emissive layer 220, a hole transport layer 225, and an anode 230. Device 200 may be fabricated by depositing the layers described, in order. Because the most common OLED configuration has a cathode disposed over the anode, and device 200 has cathode 215 disposed under anode 230, device 200 may be referred to as an “inverted” OLED. Materials similar to those described with respect to device 100 may be used in the corresponding layers of device 200. FIG. 2 provides one example of how some layers may be omitted from the structure of device 100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided by way of non-limiting example, and it is understood that embodiments of the invention may be used in connection with a wide variety of other structures. The specific materials and structures described are exemplary in nature, and other materials and structures may be used. Functional OLEDs may be achieved, by combining the various layers described in different ways, or layers may be omitted entirely, based on design, performance, and cost factors. Other layers not specifically described may also be included. Materials other than those specifically described may be used. Although many of the examples provided herein describe various layers as comprising a single material, it is understood that combinations of materials, such as a mixture of host and dopant, or more generally a mixture, may be used. Also, the layers may have various sublayers. The names given to the various layers herein are not intended to be strictly limiting. For example, in device 200, hole transport layer 225 transports holes and injects holes into emissive layer 220, and may be described as & hole transport layer or a hole injection layer. In one embodiment, an OLED may be described as having an “organic layer” disposed between a cathode and an anode. This organic layer may comprise a single layer, or may further comprise multiple layers of different organic materials as described, for example, with respect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used, such as OLEDs comprised of polymeric materials (PLEDs) such as disclosed, in U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated by reference in its entirety. By way of further example, OLEDs having a single organic layer may be used. OLEDs may be stacked, for example as described in U.S. Pat. No. 5,707,745 to Forrest et al, which is incorporated by reference in its entirety. The OLED structure may deviate from the simple layered structure illustrated in FIGS. 1 and 2. For example, the substrate may include an angled reflective surface to improve out-coupling, such as a mesa structure as described in U.S. Pat. No. 6,091,195 to Forrest et al., and/or a pit structure as described in U.S. Pat. No. 5,834,893 to Bulovie et al., which are incorporated by reference in their entireties.

Unless otherwise specified, any of the layers of the various embodiments may be deposited by any suitable method. For the organic layers, preferred methods include, thermal evaporation, ink-jet, such as described in U.S. Pat. Nos. 6,013,982 and 6,087,196, which are incorporated by reference in their entireties, organic vapor phase deposition (OVPD), such as described in U.S. Pat. No. 6,337,102 to Forrest et al., which is incorporated by reference in its entirety, and deposition by organic vapor jet printing (OVJP), such as described in U.S. Pat. No. 7,431,968, which is incorporated by reference in its entirety. Other suitable deposition, methods include spin coating and other solution based processes. Solution based processes are preferably carried out in nitrogen or an inert atmosphere. For the other layers, preferred methods include thermal evaporation. Preferred patterning methods include deposition through a mask, cold welding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819, which are incorporated by reference in their entireties, and patterning associated with some of the deposition methods such as ink-jet and OVJD. Other methods may also be used. The materials to be deposited may be modified to make them compatible with a particular deposition method. For example, substituents such as alkyl and aryl groups, branched or unbranched, and preferably containing at least 3 carbons, may be used in small molecules to enhance their ability to undergo solution processing. Substituents having 20 carbons or more may be used, and 3-20 carbons is a preferred range. Materials with asymmetric structures may have better solution processibility than those having symmetric structures, because asymmetric materials may have a lower tendency to recrystallize. Dendrimer substituents may be used to enhance the ability of small molecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the present invention may further optionally comprise a barrier layer. One purpose of the barrier layer is to protect the electrodes and organic layers from damaging exposure to harmful species in the environment including moisture, vapor and/or gases, etc. The barrier layer may be deposited over, under or next to a substrate, an electrode, or over any other parts of a device including an edge. The barrier layer may comprise a single layer, or multiple layers. The barrier layer may be formed by various known chemical vapor deposition techniques and may include compositions having a single phase as well as compositions having multiple phases. Any suitable material or combination of materials may be used for the barrier layer. The barrier layer may incorporate an inorganic or an organic compound or both. The preferred barrier layer comprises a mixture of a polymeric material and a non-polymeric material, as described in U.S. Pat. No. 7,968,146, PCT Pat. Application. Nos. PCT/US2007/023098 and PCT/US2009/042829, which are herein incorporated by reference in their entireties. To be considered a “mixture”, the aforesaid polymeric and non-polymeric materials comprising the barrier layer should be deposited under the same reaction conditions and/or at the same time. The weight ratio of polymeric to non-polymeric material may be in the range of 95:5 to 5:95. The polymeric material and the non-polymeric material may be created from the same precursor material. In one example, the mixture of a polymeric material and a non-polymeric material consists essentially of polymeric silicon and inorganic silicon.

Devices fabricated in accordance with embodiments of the invention may be incorporated into a wide variety of consumer products, including flat panel displays, computer monitors, medical monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads up displays, fully transparent displays, flexible displays, laser printers, telephones, cell phones, personal digital assistants (PDAs), laptop computers, digital cameras, camcorders, viewfinders, micro-displays, 3-D displays, vehicles, a large area wall, theater or stadium screen, or a sign. Various control mechanisms may be used to control devices fabricated in accordance with the present invention, including passive matrix and active matrix. Many of the devices are intended for use in a temperature range comfortable to humans, such as 18 degrees C. to 30 degrees C., and more preferably at room temperature (20-25 degrees C.), but could be used outside this temperature range, for example, from −40 degree C. to +80 degree C.

The materials and structures described herein may have applications in devices other than OLEDs. For example, other optoelectronic devices such as organic solar cells and organic photodetectors may employ the materials and structures. More generally, organic devices, such as organic transistors, may employ the materials and structures.

The terms halo, halogen, alkyl, cycloalkyl, alkenyl, alkynyl, aralkyl, heterocyclic group, aryl, aromatic group, and heteroaryl are known to the art, and are defined in U.S. Pat. No. 7,279,704 at cols. 31-32, which are incorporated herein by reference.

As used herein, “substituted” indicates that a substituent other than H is bonded to the relevant carbon. Thus, where R^(B) is monosubstituted, then one R^(B) must be other than H. Similarly, where R^(C) is disubstituted, then two of R^(C) must be other than H. Similarly, where R^(B) is unsubstituted R^(B) is hydrogen for all available positions.

According to an embodiment, phosphorescent compounds with fused ring substitutions that are unexpectedly suited as yellow and green emitters are provided. In has been unexpectedly determined that attaching a pendant fused ring on Ring A of compounds of Formula I, produces a new class of yellow/green phosphorescent emitters exhibiting improved properties. Comparable compounds exhibited an undesirable red shift so this result was completely unexpected.

For example, it was disclosed in US2011227049 that the following compound gave a green emission at around 528 nm.

Without the methyl substitution, the compound gave a yellow emission at around 545 nm. The methyl substitution twisted the phenyl group out of plane and disrupted the conjugation, giving a much blue shifted emission. In the compounds described herein, a fused ring substitution was introduced instead of the phenyl group. Fused aromatic or hetero aromatic substitution has lower triplet values and is expected to significantly red shift the emission compared to the phenyl substitution. However, it was discovered that these compounds did not show significant red shift, which unexpectedly makes them viable candidates as green phosphorescent emitters.

According to one embodiment, a compound comprising a ligand L having the structure according to Formula I is provided:

-   -   wherein B is a 5 or 6-membered carbocyclic or heterocyclic ring;     -   wherein C is a condensed aromatic ring system having at least         two carbocyclic or heterocyclic rings;     -   wherein A-B represents a bonded pair of carbocyclic or         heterocyclic rings coordinated to a metal M via a nitrogen atom         in ring A and an sp² hybridized atom X⁶ in ring B;     -   wherein A-C represents a bonded pair of carbocyclic or         heterocyclic rings;     -   wherein R^(C) may represent mono, di, or tri substitutions, or         no substitution;     -   wherein R^(B) may represent any number of substitution from mono         to up to the maximum possible number of substitution on ring B,         or no substitution;     -   wherein R^(C) may represent any number of substitution from mono         to up to the maximum possible number of substitution on ring C,         or no substitution;     -   wherein R^(A), R^(B), and R^(C) are independently selected from         the group consisting of hydrogen, deuterium, halide, alkyl,         cycloalkyl, heteroalkyl, aralkyl, alkoxy, aryloxy, amino, silyl,         alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl,         acyl, carbonyl, carboxylic acids, ester, nitrite, isonitrile,         sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations         thereof;     -   wherein X¹, X², X³, X⁴, X⁵, and X⁶ are independently selected         from carbon and nitrogen;     -   wherein X⁷ is carbon;     -   wherein at least one of R^(A) and R^(C) substituents adjacent to         the bond between A and C is not hydrogen; and     -   wherein the ligand L is coordinated to the metal M having an         atomic number greater than 40.

In some embodiments, ring A can be pyridine. In some embodiments, ring B can be phenyl.

In some embodiments, only one of the R^(A) and R^(C) substituents adjacent to the bond between A and C is not hydrogen. In some embodiments, the R^(A) and R^(C) substituents adjacent to the bond between A and C are selected from the group consisting of hydrogen; deuterium; linear, branched and cyclic alkyl; and combinations thereof. The R^(A) and R^(C) substituents adjacent to the bond between A and C can be selected from the group consisting of hydrogen, deuterium, methyl, ethyl, propyl, 1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl, pentyl 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, cyclopentyl, cyclohexyl, and combinations thereof. In some instances, the only one of R^(A) and R^(C) substituents adjacent to the bond between A and C that is not hydrogen, can be selected from the group consisting of deuterium, methyl, ethyl, and combinations thereof.

In some embodiments, the compound can have the formula:

-   -   wherein L′ is monoanionic bidentate ligand; and     -   wherein n is at least 1.

In some embodiments, n is 1, while n can be 2 in other embodiments.

In some more specific embodiments, L′ can be selected from the group consisting of:

wherein: Y₁, Y₂ and Y₃ are C or N,

-   -   ring E and ring F are 5-membered or 6-membered carbocycle or         heterocycle,     -   R′, R″, and R′″ are independently selected from the group         consisting of hydrogen, alkyl, alkoxy, amino, alkenyl, alkynyl,         aralkyl, aryl, and heteroaryl,     -   X is selected from the group consisting of S, NZ, O, Se, BZ,         CZZ′, and C═O,     -   Z and Z′ are independently selected from the group consisting of         hydrogen, alkyl, and aryl, and

R′, R″, and R′″ can join to form one or more fused rings.

In some particular embodiments, L′ can be

In some embodiments, the compounds described herein can be heteroleptic, while the compounds can be homoleptic in other embodiments. In some embodiments, the bond between A and C can be formed between X² and X⁷ (meta substitution relative to N in ring A), in other embodiments, the bond between A and C can be formed between X³ and X⁷ (para substitution relative to N in ring A).

In some embodiments, ring C can be selected from the group consisting of:

-   -   wherein A¹ to A⁸, Q¹ to Q⁶, B¹ to B⁸, J¹ to J¹², K¹ to K¹⁰ are         independently selected from the group consisting of C and N;     -   wherein X and Y are independently selected from the group         consisting of O, S, NR′, and CR″R′″; and     -   wherein R′, R″, and R′″ are independently selected from the         group consisting of hydrogen, deuterium, halide, alkyl,         cycloalkyl, heteroalkyl, aralkyl, alkoxy, aryloxy, amino, silyl,         alkenyl, cycloalkenyl, heteroalkenyl alkynyl, aryl, heteroaryl,         acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile,         sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations         thereof.

In some more specific embodiments, ring C can be selected from the group consisting of:

In some specific embodiments, the compound can be selected from the group consisting of:

According to another aspect of the present disclosure, a first device is also provided. The first device includes a first organic light emitting device, that includes an anode, a cathode, and an organic layer disposed between the anode and the cathode. The organic layer may include a host and a phosphorescent dopant. The organic layer can include a compound having a ligand L according to Formula I, and its variations as described herein.

The first device can be one or more of a consumer product, an organic light-emitting device and a lighting panel. The organic layer can be an emissive layer and the compound can be an emissive dopant in some embodiments, while the compound can be a non-emissive dopant in other embodiments.

In some embodiments, the organic layer can include a host. In some embodiments, the host can include a metal, complex. The host can be a triphenylene containing benzo-fused thiophene or benzo-fused furan. Any substituent in the host can be an unfused substituent independently selected from the group consisting of C_(n)H_(2n+1), OC_(n)H_(2n+1), OAr₁, N(C_(n)H_(2n+1))₂. N(Ar₁)(Ar₂), CH═CH—C_(n)H_(2n+1), C≡C—C_(n)H_(2n+1), Ar₁, Ar₁—Ar₂, C_(n)H_(2n)—Ar₁, or no substitution. In the preceding substituents n can range from 1 to 10; and Ar₁ and Ar₂ can be independently selected from the group consisting of benzene, biphenyl, naphthalene, triphenylene, carbazole, and heteroaromatic analogs thereof.

The host can be a compound selected from the group consisting of carbazole, dibenzothiphene, dibenzofuran, dibenzoselenophene, azacarbazole, aza-dibenzothiophene, aza-dibenzofuran, and aza-dibenzoselenophene. The “aza” designation in the fragments described above, i.e., aza-dibenzofuran, aza-dibenzonethiophene, etc., means that one or more of the C—H groups in the respective fragment can be replaced by a nitrogen atom, for example, and without any limitation, azatriphenylene encompasses both dibenzo[f,h]quinoxaline and dibenzo[f,h]quinoline. One of ordinary skill in the art can readily envision other nitrogen analogs of the aza-derivatives described above, and all such analogs are intended to be encompassed by the terms as set forth herein. The host can include a metal complex. The host can be a specific compound selected from the group consisting of:

and combinations thereof.

In yet another aspect of the present disclosure, a formulation that includes a compound having a ligand L according to Formula I, and its variations as described herein. The formulation can include one or more components selected from the group consisting of a solvent, a host, a hole injection material, bole transport material, an electron transport layer material (see below).

Combination with Other Materials

The materials described herein as useful for a particular layer in an organic light emitting device may be used in combination with a wide variety of other materials present in the device. For example, emissive dopants disclosed herein may be used in conjunction with a wide variety of hosts, transport layers, blocking layers, injection layers, electrodes and other layers that may be present. The materials described or referred to below are non-limiting examples of materials that may be useful in combination with the compounds disclosed herein, and one of skill in the art can readily consult the literature to identify other materials that may be useful in combination.

HIL/HTL

A hole injecting/transporting material to be used in the present invention Is not particularly limited, and any compound may be used as long as the compound is typically used as a hole injecting/transporting material. Examples of the material include, but not limit to: a phthalocyanine or porphryin derivative; an aromatic amine derivative; an indolocarbazole derivative; a polymer containing fluorohydrocarbon; a polymer with conductivity dopants; a conducting polymer, such as PEDOT/PSS; a self-assembly monomer derived from compounds such as phosphonic acid and silane derivatives; a metal oxide derivative, such as MoO_(x); a p-type semiconducting organic compound, such as 1,4,5,8,9,12-Hexaaxatriphenylenehexacarbonitrile; a metal complex, and across-linkable compounds.

Examples of aromatic amine derivatives used in HIL, or HTL include, but not limit to the following general structures:

Each of Ar¹ to Ar⁹ is selected from the group consisting aromatic hydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, azulene; group consisting aromatic heterocyclic compounds such as dibenzothiophene, dibenzofuran, dihenzoselenophene, furan, thiophene, benzofuxan, benzothiophene, benzoselenophene, carbazole, indolocarbazole, pyridylindole, pyrrolodipyrldine, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyriraidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole, henzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine, thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine; and group consisting 2 to 10 cyclic structural units which are groups of the same type or different types selected from the aromatic hydrocarbon cyclic group and the aromatic heterocyclic group and are bonded to each other directly or via at least one of oxygen atom, nitrogen atom, sulfur atom, silicon atom, phosphorus atom, boron atom, chain structural unit and the aliphatic cyclic group. Wherein each Ar is further substituted by a substituent selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, aralkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrite, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one aspect, Ar¹ to Ar⁹ is independently selected from the group consisting of:

k is an integer from 1 to 20; X¹⁰¹ to X¹⁰⁸ is C (including CH) or N; Z¹⁰¹ is NAr¹, O, or S; Ar¹ has the same group defined above.

Examples of metal complexes used in HIL or HTL include, but not limit to the following general formula:

Met is a metal, which can have an atomic weight greater than 40; (Y¹⁰¹-Y¹⁰²) is a bidentate ligand, Y¹⁰¹ and Y¹⁰² are independently selected from C, N, O, P, and S; L¹⁰¹ is an ancillary ligand; k′ is an integer value from 1 to the maximum number of ligands that may be attached to the metal; and k′+k″ is the maximum number of ligands that may be attached to the metal.

In one aspect, (Y¹⁰¹-Y¹⁰²) is a 2-phenylpyridine derivative.

In another aspect, (Y¹⁰¹-Y¹⁰²) is a carbene ligand.

In another aspect, Met is selected from Ir, Pt, Os, and Zn.

In a further aspect, the metal complex has a smallest oxidation potential in solution vs. Fc⁺/Fc couple less than about 0.6 V.

Host

The light emitting layer of the organic EL device of the present invention preferably contains at least a metal complex as light emitting material, and may contain a host material using the metal complex as a dopant material. Examples of the host material are not particularly limited, and any metal complexes or organic compounds may be used as long as the triplet energy of the host is larger than that of the dopant. While the Table below categorizes host materials as preferred for devices that emit various colors, any host material may be used with any dopant so long as the triplet criteria is satisfied.

Examples of metal complexes used as host are preferred to have the following general formula:

Met is a metal; (Y¹⁰³-Y¹⁰⁴) is a bidentate ligand, Y¹⁰³ and Y¹⁰⁴ are independently selected from C, N, O, P, and S; L¹⁰¹ is an another ligand: k′ is an integer value from 1 to the maximum number of ligands that may be attached to the metal; and k′+k″ is the maximum number of ligands that may be attached to the metal.

In one aspect, the metal, complexes are:

(O—N) is a bidentate ligand, having metal, coordinated to atoms O and N.

In another aspect, Met is selected from Ir and Pt.

In a further aspect, (Y¹⁰³-Y¹⁰⁴) is a carbene ligand.

Examples of organic compounds used as host are selected from the group consisting aromatic hydrocarbon, cyclic compounds such as benzene, biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, azulene, group consisting aromatic heterocyclic compounds such as dibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiopnene, benzofuran, benzothiopbene, benzoselenophene, carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benxothienopyridine, thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine; and group consisting 2 to 10 cyclic structural units which are groups of the same type or different types selected from the aromatic hydrocarbon cyclic group and the aromatic heterocyclic group and are bonded to each other directly or via at least one of oxygen atom, nitrogen atom, sulfur atom, silicon atom, phosphorus atom, boron atom, chain structural unit and the aliphatic cyclic group. Wherein each group is further substituted by a substituent selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, aralkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl sulfonyl phosphino, and combinations thereof.

In one aspect, host compound contains at least one of the following groups in the molecule:

R¹⁰¹ to R¹⁰⁷ is independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, aralkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, when it is aryl or heteroaryl, it has the similar definition as Ar's mentioned above.

k is an integer from 0 to 20 or 1 to 20; k′″ is an integer from 0 to 20.

X¹⁰¹ to X¹⁰⁸ is selected from C (including CH) or N.

Z¹⁰¹ and Z¹⁰² is selected from NR¹⁰¹, O, or S.

HBL

A hole blocking layer (HBL) may be used to reduce the number of holes and/or excitons that leave the emissive layer. The presence of such a blocking layer in a device may result in substantially higher efficiencies as compared to a similar device lacking a blocking layer. Also, a blocking layer may be used to confine emission to a desired region of an OLED.

In one aspect, compound used in HBL contains the same molecule or the same functional groups used as host described above.

In another aspect, compound used in HBL contains at least one of the following groups in the molecule:

k is an integer from 1 to 20; L¹⁰¹ is an another ligand, k′ is an integer from 1 to 3.

ETL

Electron, transport layer (ETL) may include a material capable of transporting electrons. Electron transport layer may be intrinsic (undoped), or doped. Doping may be used to enhance conductivity. Examples of the ETL material are not particularly limited, and any metal complexes or organic, compounds may be used as long as they are typically used to transport electrons.

In one aspect, compound used in ETL contains at least one of the following groups in the molecule:

R¹⁰¹ is selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, aralkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrite, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, when it is aryl or heteroaryl, it has the similar definition as Ar's mentioned above.

Ar¹ to Ar³ has the similar definition as Ar's mentioned above.

k is an integer from 1 to 20.

X¹⁰¹ to X¹⁰⁸ is selected, from C (including CH) or N.

In another aspect, the metal complexes used in ETL contain, but not limit to the following general formula:

(O—N) or (N—N) is a bidentate ligand, having metal coordinated to atoms O, N or N, N; L¹⁰¹ is another ligand; k′ is an integer value from 1 to the maximum number of ligands that may be attached to the metal.

In any above-mentioned compounds used in each layer of the OLED device, the hydrogen atoms can be partially or fully deuterated. Thus, any specifically listed substituent, such as, without limitation, methyl, phenyl, pyridyl, etc. encompasses undeuterated, partially deuterated, and fully deuterated versions thereof. Similarly, classes of substituents such as, without limitation, alkyl, aryl, cycloalkyl, heteroaryl, etc. also encompass undeuterated, partially deuterated, and fully deuterated versions thereof.

In addition to and/or in combination with the materials disclosed herein, many hole injection materials, hole transporting materials, host materials, dopant materials, exiton/hole blocking layer materials, electron transporting and electron injecting materials may be used in an OLED. Non-limiting examples of the materials that may be used in an OLED in combination with materials disclosed herein are listed in Table 1 below. Table 1 lists non-limiting classes of materials, non-limiting examples of compounds for each class, and references that disclose the materials.

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EP650955

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US20070278938, US20080106190 US20110163302 Indolocarbazoles

Synth. Met. 111, 421 (2000) Isoindole compounds

Chem. Mater. 15, 3148 (2003) Metal carbene complexes

US20080018221 Phosphorescent OLED host materials Red hosts Arylcarbazoles

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Nature 395, 151 (1998)

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WO2005014551

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WO2010056066 Chrysene based compounds

WO2011086863 Green hosts Arylcarbazoles

Appl. Phys. Lett. 78, 1622 (2001)

US20030175553

WO2001039234 Aryltriphenylene compounds

US20060280965

US2006280965

WO2009021126 Poly-fused heteroaryl compounds

US20090309488 US20090302743 US20100012931 Donor acceptor type molecules

WO2008056746

WO2010107244 Aza-carbazole/DBT/DBF

JP2008074939

US20100187984 Polymers (e.g., PVK)

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WO2004093707 Metal phenoxybenzooxazole compounds

WO2005089025

WO2006132173

JP200511610 Spirofluorene-carbazole compounds

JP2007254297

JP2007254297 Indolocabazoles

WO2007063796

WO2007063754 5-member ring electron deficient heterocycles (e.g., triazoles, oxadiazole)

J. Appl. Phys. 90, 5048 (2001)

WO2004107822 Tetraphenylene complexes

US20050112407 Metal phenoxypyridine compounds

WO2005030900 Metal coordination complexes (e.g., Zn, Al with N{circumflex over ( )}N ligands)

US20040137268, US20040137267 Blue hosts Arylcarbazoles

Appl. Phys. Lett. 82, 2422 (2003)

US20070190359 Dibenzothiophene/ Dibenzofuran-carbazole compounds

WO2006114966, US20090167162

US20090167162

WO2009086028

US20090030202, US20090017330

US20100084966 Silicon aryl compounds

US20050238919

WO2009003898 Silicon/Germanium aryl compounds

EP2034538A Aryl benzoyl ester

WO2006100298 Carbazole linked by non- conjugated groups

US20040115476 Aza-carbazoles

US20060121308 High triplet metal organometallic complex

US7154114 Phosphorescent dopants Red dopants Heavy metal porphyrins (e.g., PtOEP)

Nature 395, 151 (1998) Iridium(III) organometallic complexes

Appl. Phys. Lett. 78, 1622 (2001)

US2006835469

US2006835469

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US20060202194

US20070087321

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US20070087321

Adv. Mater. 19, 739 (2007)

WO2009100991

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US20070103060 Osminum(III) complexes

Chem. Mater. 17, 3532 (2005) Rutheniium(II) complexes

Adv. Mater. 17, 1059 (2005) Rhenium (I), (II), and (III) complexes

US20050244673 Green dopants Iridium(III) organometallic complexes

Inorg. Chem. 40, 1704 (2001) and its derivatives

US20020034656

US7332232

US20090108737

WO2010028151

EP1841834B

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US20090039776

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Chem. Mater. 16, 2480 (2004)

US20070190359

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WO2010086089, WO2011044988

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Angew. Chem. Int. Ed. 2006, 45, 7800

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US20090165846

US20080015355

US20010015432

US20100295032 Monomer for polymeric metal organometallic compounds

US7250226, US7396598 Pt(II) organometallic complexes, including polydentated ligands

Appl. Phys. Lett. 86, 153505 (2005)

Appl. Phys. Lett. 86, 153505 (2005)

Chem . Lett. 34, 592 (2005)

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US20060263635

US20060182992 US20070103060 Cu complexes

WO2009000673

US20070111026 Gold complexes

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Inorg. Chem. 42, 1248 (2003) Osmium(II) complexes

US7279704 Deuterated organometallic complexes

US20030138657 Organometallic complexes with two or more metal centers

US20030152802

US7090928 Blue dopants Iridium(III) organometallic complexes

WO2002002714

WO2006009024

US20060251923 US20110057559 US20110204333

US7393599, WO2006056418, US20050260441, WO2005019373

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Inorg. Chem. 46, 4308 (2007)

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WO2005123873

WO2007004380

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US7279704

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US7655323 Exciton/hole blocking layer materials Bathocuprine compounds (e.g., BCP, BPhen)

Appl. Phys. Lett. 75, 4 (1999)

Appl. Phys. Lett. 79, 449 (2001) Metal 8-hydroxyquinolates (e.g., BAlq)

Appl. Phys. Lett. 81, 162 (2002) 5-member ring electron deficient heterocycles such as triazole, oxadiazole, imidazole, benzoimidazole

Appl. Phys. Lett. 81, 162 (2002) Triphenylene compounds

US20050025993 Fluorinated aromatic compounds

Appl. Phys. Lett. 79, 156 (2001) Phenothiazine-S-oxide

WO2008132085 Silylated five-membered nitrogen, oxygen, sulfur or phosphorus dibenzoheterocycles

WO2010079051 Aza-carbozoles

US20060121308 Electron transporting materials Anthracene- benzoimidazole compounds

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US20090115316 Anthracene-benzothiazole compounds

Appl. Phys. Lett. 89, 063504 (2006) Metal 8-hydroxyquinolates (e.g., Alq₃, Zrq₄)

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Appl. Phys. Lett. 74, 865 (1999)

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EXPERIMENTAL Device Examples

All example devices were fabricated by high, vacuum (<10⁻⁷ Torr) thermal evaporation. The anode electrode was 1200 Å of indium tin oxide (ITO). The cathode consisted of 10 Å of LiF followed by 1,000 Å of Al. All devices were encapsulated with a glass lid sealed with an epoxy resin in a nitrogen glove box (<1 ppm of H₂O and O₂) immediately after fabrication, and a moisture getter was incorporated Inside the package.

The organic stack of the device examples consisted of sequentially, from the ITO surface, 100 Å of Compound A as the hole injection layer (HIL), 300 Å of 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (α-NPD) as the hole transporting layer (HTL), 300 Å of the inventive compounds doped with Compound B as host, with 8-10 wt % of the iridium phosphorescent compound as the emissive layer (EML), 50 or 100 Å of Compound B as a blocking layer (BL), 400 or 450 Å of Alq (tris-8-hydroxyquinoline aluminum) as the ETL. The comparative Examples were fabricated similarly to the Device Examples except that Compound A was used as the emitter in the EML.

The device results and data are summarized in Tables 1 and 2 from those devices.

TABLE 1 device Structures of Inventive Compound and Comparative Compound HIL HTL EML Example (100 Å) (300 Å) (300 Å, doping %) BL ETL Example 1 Compound A NPD Compound 1 (10%) Compound B Alq  (50 Å) (450 Å) Example 2 Compound A NPD Compound 2 (10%) Compound B Alq  (50 Å) (450 Å) Example 3 Compound A NPD Compound 20 (10%) Compound B Alq (100 Å) (400 Å) Example 4 Compound A NPD Compound 21 (10%) Compound B Alq  (50 Å) (450 Å) Example 5 Compound A NPD Compound 39 (10%) Compound B Alq (100 Å) (400 Å) Example 6 Compound A NPD Compound 40 (10%) Compound B Alq (100 Å) (400 Å) Comparative Compound A NPD Compound A (10%) Compound B Alq Example 1  (50 Å) (450 Å)

TABLE 2 VTE Device Results Rela- Rela- Relative Relative λ_(max) tive tive Initial LT80 x y (nm) Voltage EQE Luminance % Example 1 0.338 0.616 528 1.1 0.9 0.8 0.8 Example 2 0.329 0.619 526 1.1 0.9 0.9 0.4 Example 3 0.391 0.583 538 1.3 0.9 0.8 1.3 Example 4 0.364 0.606 534 1.0 1.1 1.1 0.7 Example 5 0.357 0.607 532 1.1 0.8 0.9 0.7 Example 6 0.342 0.618 528 1.0 1.0 1.0 0.5 Compara- 0.336 0.620 526 1.0 1.0 1.0 1.0 tive Example 1

Table 2 summaries the performance of the devices. The CIE coordinates, driving voltage (V), and external quantum efficiency (EQE) were measured at 1000 nits, while the lifetime (LT_(80%)) was defined as the time required for the device to decay to 80% of its initial luminance under a constant current density of 40 mA/cm². As can be seen from the table, despite the fused ring substitution, the inventive compounds unexpectedly produced similar colors to the comparative example while still maintaining higher efficiency and longer device lifetime, which make them suitable for commercial applications as green emitters for display and lighting.

It is understood that the various embodiments described herein are by way of example only, and are not intended to limit the scope of the invention. For example, many of the materials and structures described herein may be substituted with other materials and structures without deviating from the spirit of the invention. The present invention as claimed may therefore Include variations from the particular examples and preferred embodiments described herein, as will be apparent to one of skill in the art. It is understood that various theories as to why the invention works are not intended to be limiting. 

We claim:
 1. A heteroleptic compound having a structure of Formula II:

wherein n is 1 or 2; wherein B is a 5 or 6-membered carbocyclic or heterocyclic ring; wherein C is a condensed aromatic ring system having at least two carbocyclic or heterocyclic rings; wherein A-B represents a bonded pair of carbocyclic or heterocyclic rings coordinated to Ir via a nitrogen atom in ring A and an sp² hybridized atom X⁶ in ring B; wherein A-C represents a bonded pair of carbocyclic or heterocyclic rings; wherein R^(A) may represent mono, di, or tri substitutions, or no substitution; wherein R^(B) may represent any number of substitution from mono to up to the maximum possible number of substitution on ring B, or no substitution; wherein R^(C) may represent any number of substitution from mono to up to the maximum possible number of substitution on ring C, or no substitution; wherein each R^(A), R^(B), and R^(C) is independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, aralkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; wherein X¹, X², X³, and X⁴ are selected from C—R^(A), C—X⁷, and N; wherein X⁶ is selected from carbon and nitrogen; wherein X⁵ and X⁷ are carbon; wherein at least one of R^(A) and R^(C) is at least a mono-substitution; wherein at least one of R^(A) and R^(C) adjacent to the bond between A and C is not hydrogen; wherein L′ is monoanionic bidentate ligand selected from the group consisting of:

and wherein: R′, R^(2′), R″, and R′″ are independently selected from the group consisting of hydrogen, alkyl, alkoxy, amino, alkenyl, alkynyl, aralkyl, aryl, and heteroaryl, X is selected from the group consisting of S, NZ, O, Se, BZ, CZZ′, and C═O, Z and Z′ are independently selected from the group consisting of hydrogen, alkyl, and aryl, and R′, R″, and R′″ can join to form one or more fused rings.
 2. The compound of claim 1, wherein A is pyridine.
 3. The compound of claim 1, wherein B is phenyl.
 4. The compound of claim 1, wherein only one of R^(A) and R^(C) adjacent to the bond between A and C is not hydrogen.
 5. The compound of claim 1, wherein the R^(A) and R^(C) adjacent to the bond between A and C are independently selected from the group consisting of hydrogen; deuterium; linear, branched and cyclic alkyl; and combinations thereof.
 6. The compound of claim 1, wherein the R^(A) and R^(C) adjacent to the bond between A and C are independently selected from the group consisting of hydrogen, deuterium, methyl, ethyl, propyl, 1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl, pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, cyclopentyl, cyclohexyl, and combinations thereof.
 7. The compound of claim 4, wherein the only one of R^(A) and R^(C) adjacent to the bond between A and C that is not hydrogen is selected from the group consisting of deuterium, methyl, ethyl, and combinations thereof.
 8. The compound of claim 1, wherein n=1.
 9. The compound of claim 1, wherein n=2.
 10. The compound of claim 1, where L′ is


11. The compound of claim 1, wherein bond between A and C is formed between X² and X⁷.
 12. The compound of claim 1, wherein bond between A and C is formed between X³ and X⁷.
 13. The compound of claim 1, wherein C is selected from the group consisting of:

wherein A¹ to A⁸, Q¹ to Q⁶, B¹ to B⁸, J¹ to J¹², K¹ to K¹⁰ are independently selected from the group consisting of C and N; wherein X and Y are independently selected from the group consisting of O, S, NR^(3′), and CR^(3″)R^(3′″); and wherein R^(3′), R^(3″) and R^(3′″) are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, aralkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfanyl, sulfonyl, phosphino, and combinations thereof.
 14. The compound of claim 1, wherein C is selected from the group consisting of:


15. A compound selected from the group consisting of:


16. A first device comprising a first organic light emitting device, further comprising: an anode; a cathode; and an organic layer, disposed between the anode and the cathode, comprising a heteroleptic compound having a structure of Formula II:

wherein n is 1 or 2; wherein B is a 5 or 6-membered carbocyclic or heterocyclic ring; wherein C is a condensed aromatic ring system having at least two carbocyclic or heterocyclic rings; wherein A-B represents a bonded pair of carbocyclic or heterocyclic rings coordinated to Ir via a nitrogen atom in ring A and an sp² hybridized atom X⁶ in ring B; wherein A-C represents a bonded pair of carbocyclic or heterocyclic rings; wherein R^(A) may represent mono, di, or tri substitutions, or no substitution; wherein R^(B) may represent any number of substitution from mono to up to the maximum possible number of substitution on ring B, or no substitution; wherein R^(C) may represent any number of substitution from mono to up to the maximum possible number of substitution on ring C, or no substitution; wherein each R^(A), R^(B), and R^(C) independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, aralkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; wherein X¹, X², X³, and X⁴ are selected from C—R^(A), C—X⁷, and N; wherein X⁶ is selected from carbon and nitrogen; wherein X⁵ and X⁷ are carbon; wherein at least one of R^(A) and R^(C) is at least a mono-substitution; wherein at least one of R^(A) and R^(C) adjacent to the bond between A and C is not hydrogen; wherein L′ is monoanionic bidentate ligand selected from the group consisting of:

and wherein: R′, R^(2′), R″, and R′″ are independently selected from the group consisting of hydrogen, alkyl, alkoxy, amino, alkenyl, alkynyl, aralkyl, aryl, and heteroaryl, X is selected from the group consisting of S, NZ, O, Se, BZ, CZZ′, and C═O, Z and Z′ are independently selected from the group consisting of hydrogen, alkyl, and aryl, and R′, R″, and R′″ can join to form one or more fused rings.
 17. The first device of claim 16, wherein the first device is selected from the group consisting of a consumer product, an organic light-emitting device, and lighting panel.
 18. The first device of claim 16, wherein the first device is a consumer product selected from the group consisting of flat panel displays, computer monitors, medical monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads up displays, fully transparent displays, flexible displays, laser printers, telephones, cell phones, personal digital assistants (PDAs), laptop computers, digital cameras, camcorders, viewfinders, micro-displays, 3-D displays, vehicles, wall screens, theater screens, stadium screens, and signs.
 19. The first device of claim 16, wherein the organic layer is an emissive layer and the compound is an emissive dopant.
 20. The first device of claim 16, wherein the organic layer is an emissive layer and the compound is a non-emissive dopant.
 21. The first device of claim 16, wherein the organic layer further comprises a host.
 22. The first device of claim 21, wherein the host comprises a triphenylene containing benzo-fused thiophene or benzo-fused furan; wherein any substituent in the host is an unfused substituent independently selected from the group consisting of C_(n)H_(2n+1), OC_(n)H_(2n+1), OAr₁, N(C_(n)H_(2n+1))₂, N(Ar₁)(Ar₂), CH═CH—C_(n)H_(2n+1), C≡CC_(n)H_(2n+1), Ar₁, Ar₁-Ar₂, C_(n)H_(2n)—Ar₁, or no substitution; wherein n is from 1 to 10; and wherein Ar₁ and Ar₂ are independently selected from the group consisting of benzene, biphenyl, naphthalene, triphenylene, carbazole, and heteroaromatic analogs thereof.
 23. The first device of claim 21, wherein the host comprises a compound selected from the group consisting of: carbazole, dibenzothiphene, dibenzofuran, dibenzoselenophene, azacarbazole, aza-dibenzothiophene, aza-dibenzofuran, and aza-dibenzoselenophene.
 24. The first device of claim 21, wherein the host is selected from the group consisting of:

and combinations thereof.
 25. The first device of claim 21, wherein the host comprises a metal complex.
 26. A formulation comprising a compound according to claim
 1. 